Boat propellers are particularly liable to theft since boats are usually left unattended for long periods and in isolated places. The present invention has particular application to outboard motor propellers, which gives it a field of great usefulness, outboard motors, today, being widely found on boats of a size which formerly all had inboard motors. Typically, outboard motors include an upright drive shaft and housing aft of a boat's transom and a horizontal shaft, also protected by a housing, that mounts the propeller. The upright housing tapers down from the motor itself, and the horizontal housing takes the form of a horizontal bulge in the motor structure.
In a professional preliminary search of the Patent and Trademark Office files the following four patents were developed:
Reese, U.S. Pat. No. 3,759,076. A device hooks onto a lug in the sleeve portion of a propeller itself and covers the nut to prevent its removal. In this device the propeller can still be turned and the entire boat stolen by running the engine at low speed. Furthermore it relies on a particular propeller structure having lugs that will accept a hook. It will be shown that my structure provides much more positive protection and can be applied to a much wider range of propeller types, including those without sleeves.
Sims, U.S. Pat. No. 4,257,247. Here again, the device engages only the propeller itself to cover the nut. The whole boat could be stolen by driving the propeller slowly. This device has leg elements that extend from a point directly forward of the propeller blades aft to the end of the sleeve. It is not adjustable for different propellers and, of course, if the leg elements are too long the nut can be removed by an angle wrench.
Wersinger, U.S. Pat. No. 3,981,165. This device also engages only the propeller itself and does not keep it from turning, so that the entire boat can be stolen at slow speed. Like Sims, Wersinger's structure must apparently be custom fitted to each propeller.
Milewicz, U.S. Pat. No. 3,981,617. This is a device for a special nut with means to deny access to the cotter pin. The motor could be run to steal the boat. As shall be explained the concept here is remote from that of my invention.